Most of us will already be familiar with the claims that probiotics in our yoghurts might improve human digestion. Now it seems that probiotics could offer an environmentally-friendly alternative to the use of antibiotics and antimicrobials in shellfish aquaculture.
Researchers at the National Oceanic and Atmospheric Administration (NOAA) Milford Laboratory in Connecticut, have shown that naturally-occurring bacteria isolated from adult eastern oysters and northern bay scallops may be potential candidates for use in oyster larviculture.
Two related studies published in the Journal of Shellfish Research identify the probiotic bacterium (OY15), which in pilot studies has been shown to significantly improve survival during the critical first two weeks of larval life.
"We are cautiously optimistic that this probiotic candidate, OY15, will offer a number of significant benefits to the shellfish industry," said Gary Wikfors, co-author of both studies and head of the Milford Laboratory's Biotechnology Branch. "Commercial and public shellfish hatcheries can have low survival rates for shellfish seed during the first two weeks, so improving those survival rates and the health of the organisms beyond that point is a pretty significant step forward."
Bacterial diseases caused by pathogens such as Vibrio are one of the major causes of mortality in the very early larval stages of hatchery shellfish, resulting in significant financial loss for farmed shellfish, which accounts for 25% of global aquaculture.
With a growing demand for environmentally-friendly aquaculture, the use of probiotics in shellfish aquaculture is also growing. However, there is still fundamental need for further research and full-scale trials for the development of probiotics suited for aquaculture use.
"The objective of the first part of this study was to isolate and evaluate new probiotic bacteria which, when incorporated into foods used in shellfish hatcheries, might significantly improve larval survival," said co-author Diane Kapareiko, a microbiologist at the Milford Laboratory. The second part of the study was to test the new probiotic candidate on the survival of oyster larvae in pilot-scale trials during their first two weeks of life.
"We conducted a very cautious, step by step study, to identify the best candidates under a variety of scenarios," Wikfors said. "Our bench-scale challenge studies indicated that oyster larvae exposed to probiotic candidate OY15 had the highest survival rate, and that the survival of pathogen-challenged larvae was further improved by the presence of OY 15 compared to the pathogen alone. It is somewhat analogous to a human building up immunity to a certain organism by being exposed to it, but without the involvement of antibodies."
"This two-part study confirms that use of naturally-occurring probiotic bacteria confers protection to oyster larvae against bacterial disease and improves their survival," Kapareiko said. "The results can be used as guidelines for isolating and screening other potential probiotic candidates for similar aquaculture applications, and provide the basis for developing functional foods for use in shellfish hatcheries that incorporate a naturally occurring, probiotic bacteria."
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